1. Technical Field
The present invention relates to a wafer transport system and a method for operating the same. More particularly, the present invention relates to a wafer transport system with a low-capacity carrier and a method for operating the same.
2. Description of the Related Art
Recently, the applications of wafers have greatly expanded from conventional electronic industry to the other fields, such as the solar industry. Therefore, the requirement of wafers and silicon thin-films has been greatly increased in the past few years.
The conventional manufacture of wafers is composed of several production processes and fabrication tools. For example, the production processes may comprise photolithography, measuring, etching, ion implantation, and deposition; and, the production process may be completed with the cooperation of multiple fabrication tools and measurement instruments. For harmonizing these production processes and fabrication tools to increase the productive efficiency, semiconductor foundries usually integrated the automated material handling system (AMHS) into the production process to control the movement, distribution and storage of materials.
The conventional AMHS equipment include overhead hoist transfer (OHT), rail guided vehicle (RGV), overhead shuttle (OHS), automated guided vehicle (AGV), and person rail guided vehicle (PRV). The AMHS equipment usually collocates with front opening unified pods (FOUP) capable of performing batch transfer of wafers among the workstations in a fabrication plant (FAB). In some situations, such batch transfer may be accomplished artificially by a worker who transports a fully loaded FOUP from one workstation to another for further processes.
Conventional FOUPs may, based on the design, accommodate wafers or substrates in a diameter of 300 mm (12-inch) or 450 mm (18-inch). The most common FOUPs are available with a capacity of 25 wafers. The AMHS would transfer a FOUP loaded with 25 semi-processed wafers from a first workstation to a second workstation for the following procedures, and request another FOUP full of untreated wafers to enter the first workstation to initiate another production cycle. For the wafers in a FOUP, the fabrication time of one production processes comprises the time for transporting in, the time for processing all the 25 wafers, and the time for transporting out.
Several problems have emerged from conventional AMHS and known transport systems in a sub-20 nm process of the semiconductor industry. The wafers become highly sensitive to several factors in such advanced production processes where the factors are required to be precisely controlled. The problems are as follows: (1) The patterns and the active regions on a wafer are damaged and inactivated easily when expose to oxygen or moisture. (2) The patterns on wafers with increasing diameter require multiple steps of photolithography which result in a long fabrication time. Additionally, the first processed wafer in a FOUP cannot continue to the following steps unless the other 24 wafers have undergone the same procedures; therefore, the fabrication time is further elongated. (3) Invisible micro cracks are easily formed on the patterns due to collisions. Especially when large-sized wafers are stacked in a wafer pod, a lot of wafers may be crushed due to the heavy weight. (4) For protecting the wafers from environmental contaminants and atmospheric gases, the entire system constructed in a clean room is supposed to be shut down for an engineer to enter to replace or repair the apparatus in the system.
Accordingly, there is a need for a novel wafer transport system to overcome the aforementioned defects.